My prior patent discloses a centrifugal pump having a rotor, an inlet at the center of the rotor casing, and an outlet disposed at the outer periphery of the casing. In a pump of this type, pressure within the casing varies from a minimum or negative pressure at the intake eye to a maximum at the outer wall of the casing where the outlet or discharge opening is provided.
The patent disclosed means for sensing a pressure within the pump casing during operaton of the pump, and this means included a rotary plug of circular cross-section provided in the top wall of the casing having a port located eccentrically at the inner wall of the plug, so that upon rotary adjustment of the plug, the port can be adjusted radially of the casing.
In my prior patent there is disclosed a pumping system control which was designed primarily for use in discharging water from a laundry tub. The patent indicates that the pump control disclosed therein was capable of general application. In fact, since the pump control system has been in commercial production, its field of use has greatly expanded. It is now being used to evacuate water from basements, bar sinks, waste water from beauty parlors, water coolers, sauna baths, and in office buildings where individual hand wash sinks are used, and many others.
In some of its applications, such as in the case of the hand wash sinks, special problems are presented. For example in this case, as in others, the head is sometimes high and the distance to the nearest outlet is long, and it is necessary to sense the pressure within the pump at a point closely adjacent the pump intake eye, which is not possible with the angularly adjustable plug.
In other applications, such as where a low head exists, it is desirable to sense the pressure closely adjacent the periphery of the casing, at a point not possible with the angularly adjustable plug.
Accordingly the use of the angularly adjustable plug with the eccentric pressure sensing port does not afford sufficient adjusting limits to include the extreme limits required by the new uses to which the pump is applied.
There are limitations to the shape and configuration of a centrifugal pump housing in order that the pump design remains practical and efficient, and these preclude simply increasing the diameter of the eccentric plug so that its pressure sensing port may be adjusted through a range determined by its location from closely adjacent the eye of the pump at its intake to a point closely adjacent the outer periphery of the housing.
In accordance with the present invention there is provided a simple and relatively inexpensive improvement in which a sensing tube is longitudinally adjustable radially of the casing to position a pressure sensing port therein between the intake eye of the pump and the extreme outside periphery of the casing.
In addition, the present invention affords a further advantage. The tube is received in a laterally open channel for the adjustment range provided, and this will result in a flow of water along this channel and along the tube, due to the pressure gradient from the outer periphery (the pressure side) to the intake eye (the vacuum or suction side). This flow of water of course varies with the size of the channel, as well as the pressure of water being pumped against. In any case, the flow of water past the open end of the tube, creates an additional vacuum in the tube.
In some cases this additional vacuum is useful, but in other cases it is desirable to eliminate it. Where the additional vacuum is not desired, the tube is closed at its inner end, and the pressure sensing port is provided at the side of the tube closely adjacent its closed inner end. In this case the stream of water across the sensing port creates no additional vacuum, and the pressure sensitive switch which controls the pump motor responds only to a neutral zone that automatically develops as the pump reaches the empty stage.